/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/************************************************************************
 * libc/math/lib_pow.c
 *
 * This file is a part of NuttX:
 *
 *   Copyright (C) 2012 Gregory Nutt. All rights reserved.
 *   Ported by: Darcy Gong
 *
 * It derives from the Rhombs OS math library by Nick Johnson which has
 * a compatibile, MIT-style license:
 *
 * Copyright (C) 2009, 2010 Nick Johnson <nickbjohnson4224 at gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 ************************************************************************/

/************************************************************************
 * Included Files
 ************************************************************************/

#include <tinyara/compiler.h>

#include <math.h>
#include <stdint.h>

static union {
	double dbl;
	uint64_t bit;
} zero;

/************************************************************************
 * Public Functions
 ************************************************************************/

#ifdef CONFIG_HAVE_DOUBLE
/* since pow get value using exp, result of pow is not a precise value. */
double pow(double b, double e)
{
	double int_part;
	modf(e, &int_part);
	if (b > 0.0) {
		if (b == 1.0) {
			return b;
		}
		return exp(e * log(b));
	} else if (b == 0.0) {
		if (e > 0.0) {
			return b;
		} else if (e == 0.0) {
			return NAN;
		} else {
			if (e == int_part) {
				if ((int64_t)e % 2) {
					zero.dbl = b;
					if (zero.bit != (uint64_t)0x0) {
						return -INFINITY;
					}
				}
				return INFINITY;
			}
		}
	} else {
		if (e == int_part) {
			if ((int64_t)e % 2) {
				return -exp(e * log(-b));
			}
			return exp(e * log(-b));
		}
	}
	return NAN;
}
#endif
